PHPMailer
"Probably the world's most popular code for sending email from PHP!
Used by many open-source projects: WordPress, Drupal, 1CRM, SugarCRM, Yii, Joomla! and many more"

Description
An independent research uncovered a critical vulnerability in PHPMailer that could potentially be used by (unauthenticated) remote attackers to achieve remote arbitrary code execution in the context of the web server user and remotely compromise the target web application.
To exploit the vulnerability an attacker could target common website components such as contact/feedback forms, registration forms, password email resets and others that send out emails with the help of a vulnerable version of the PHPMailer class.